Construction

Historically, thatching methods and materials reflected strong, local traditions but, increasingly, techniques are becoming standardised and regional distinctiveness is being slowly eroded.

The following information explains these traditional techniques and materials, highlighting the material and regional variations and modern developments.

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Roof structure

Most underlying roof structures are formed of timber with the thatch supported by battens spanning between rafters. More rarely, instead of battens, wooden wattle panels were fixed to the rafters. In some cases, woven water reed mat (known as fleeking) served the same purpose.

A few rare examples of ‘solid’ thatched roof structures survive. Here, the thatch is carried on bundles of brushwood and the like, stacked up on top of ceiling joists to form a triangular shaped heap. The thatch was attached directly into the brushwood. The only known surviving examples have been covered with corrugated iron to protect them. All are on simple agricultural buildings, but it is known that the method was also used for humble dwellings.

Examples of historical and modern fleeking:

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Main coat

The main coat of a thatched roof is formed by fixing bundles of thatch, with their lower ends aligned, in overlapping courses from the eaves and verges upward towards the ridge, to form a thick layer (or coat). For most roofs this will be about 250-300mm (10 – 12 inches) thick, although in some techniques much thinner coats are used (see Rick thatching).

For a new thatched roof, the thatch is fixed by tying to the rafters, battens or other support. Subsequent coats can be applied over the remains of underlying coats and fixed using spars and sways or metal fixings.

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Ridges

The ridge is the apex of the roof and the style of thatching varies, depending on material, local tradition or customer choice.

The ridge is constructed using ridge rolls, sometimes known as a ‘dolly’, consisting of handfuls of straw or water reed, bound round with straw bonds or twine. By pushing more handfuls of straw or reed into the end of the bundle, and tying at regular intervals, a long, even roll can be formed. Before the top edge of the upper courses of thatch reaches the ridge, the ridge roll is placed along the ridge and tied to the ridge piece or the battens on either side of it. As thatching continues, the tops of the upper courses of thatch which oversail the ridge are either twisted and sparred down into the ridge roll (long straw and combed wheat reed) or fixed with sways and trimmed flush with the opposing roof slope (water reed). In this way the height of the ridge is built up. Depending on the material being used, there may be only one ridge roll, or several, each of diminishing size to help form a narrow apex to the ridge. On some roofs, mortar was used to build up the height and increase the pitch of the ridge.

Ridges are most commonly of straw (both as long straw and combed wheat reed) or sedge, both of which are pliable.

There are two basic types of ridge:

  • The wrap-over method
    The thatch is bent or wrapped over the apex of the roof and secured on either side with spars and liggers. Typically used for long straw thatching and found primarily in the East, South-East and the Midlands and…
  • The butt-up method
    A butt-up ridge is made from combed wheat reed, laid so that the butt ends of the material placed on either side of the roof meet at the apex and are tightly butted together to form a watertight seal. The ridge is then secured either side with spars and liggers. Typically used on combed wheat reed roofs and found more commonly in the South-West.

There are various distinct regional variations to both types. Click here for regional variations.

Flush or Block styles
Both types of ridge can be finished in either a flush or block style and can be decorated with liggers and spars.

A flush ridge is formed when the ends of the material forming the ridge are sheared or trimmed off flush with the main coat of thatch. They are commonly associated with long straw and combed wheat reed roofs.

A block ridge is formed when an extra layer or skirt of ridging material is used to form a block relief, raised approximately 10mm (4 inches) from the surface of the main thatch. This extra thickness can then be cut either straight or with ornamental patterns such as semi-circles (scalloped) or points (dragon’s teeth).

Historical research has shown that early ridges were usually finished flush with the main coat, and were not elaborately decorated with liggerwork.

Knuckle ridge
A type of ridge used historically but rarely seen in England nowadays is known as a rope ridge or knuckle ridge. Handfuls of straw were twisted together to form a tight loop (or ‘knuckle’), which is placed on the apex of the ridge with the loose ends fixed down on either side with liggers and spars. When the work is complete the effect is of a thick straw rope stretched the length of the ridge.
Eaves & Verges
For water reed and combed wheat reed, it is important that the thatch kicks up at the eaves and verges, to help to tension the material in its fixings. Where the rafter feet are positioned towards the inner face of the wall, the outer edge of the wall provides the eaves kick. Alternatively, various materials and methods could be used to raise the eaves and create a tilt: cob (south west), mortar fillets, reed rolls or barge boards.

After thatching, combed wheat reed is trimmed with an eaves hook, to form a neat straight line at the eaves and verge. The verges are undercut to form an overhanging profile in which the upper edge formed a drip, shedding water as far as possible from the wall. Water reed is too strong to be cut, so the eaves and verges are formed by dressing into place with the leggett. This results in a squared verge profile in which the drip point is closer to the wall. In the drier climate of the south east this was probably acceptable, but where water reed is used in the south west, it tends to be dressed to for an undercut profile similar to that of a traditional combed wheat reed verge.

The eaves and verges of long straw roofs are cut using a knife or a pair of shears. Long straw is not fixed under tension and the eaves and verges are less stiff than combed wheat reed or water reed. Additional resistance to wind lift was provided by liggers sparred into the thatch. In some East Anglian counties, the long straw was ‘rolled’ over the verge and secured with spars and liggers.

On some roofs, thatch was fixed over stone slate, slate or tiled eaves courses.

Valleys
Additional material is used to pack out valleys to form a broad, rounded shape that distributes run-off, rather than a sharp angle which would concentrate rainfall and encourage erosion.Alternatively, valleys may be made in lead, which is more durable but is liable to become clogged with thatch debris. The lead is best applied by an experienced leadworker. To find out more information on leadwork professionals, follow the link to the Association of Leadwork Professionals.

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Fixings

Thatch was traditionally fixed down by clamping the bundles to roof timbers. Sways (long hazel or willow rods, about 2-3cm (1 inch) in diameter) were laid across the bundles of thatch and held in place with twine or rope passed down through the thatch by means of a hook or large ‘needle’ and tied round the support. In the earliest roofs, plant stems were used, but by the 18th century hemp rope or twine (sometimes tarred to discourage damage by rodents) became the norm.

From the 1960s, steel crooks and rods and polypropylene baler twine were increasingly used, although many thatchers prefer the traditional fixings.

For re-coating thatch, the sways could be clamped in place using spars. These are lengths of split hardwood, usually hazel or willow, approximately 750mm long and 13mm in diameter, twisted into a hairpin shape, and also known as brotches, broaches or spicks. When driven into the base coats the prongs spring apart gripping the thatch. Since the late 20th century, plastic spars have also been used. Instead of sways, a thick rope made from straw or reed (known as ‘bond’ or ‘scud’) was often used.

Ridges are secured with liggers (similar to spars, but un-bent) held down by spars.

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Abutments

At abutments with other building elements, such as chimneys or dormer windows, measures are required to make the junction weathertight. Traditionally, lime mortar flaunchings were used, but in the 20th century , lead flashings became common. Thatchers usually apply mortar fillets themselves, but correct installation of lead flashings may require the services of a leadworker.

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Netting

Wire netting was introduced in the late 19th century to provide additional protection from birds and rodents. Nowadays, plastic netting is often used. Netting can be applied to either just the ridge or over the entire roof. When applied over the main coat, there is some evidence that it may trap debris that can accelerate the rate of decay, and if not fixed correctly, it can hamper removal of thatch in the event of a fire (see Fire). Unfortunately netting is often attached routinely, even when there is no history of the roof being attacked by wildlife.

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Fire resistant boards, roofing felts and membranes

Traditional thatched roofs are vapour permeable so moisture from within a property can be transmitted through the material into the outside atmosphere. In the last quarter of the 20th century, efforts to improve fire resistance and minimise heat loss, led to a trend in installing sarking felt, polythene sheeting and fire-resistant boards.

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Internal Finishes to Thatched Roofs

Some thatched roofs are open to the underside of the rafters, but where the space under the roof is used for habitable accommodation then internal finishes are normally applied either over the rafters or between them.

Examples that may be found:

  • Torching: Mortar-coating applied to the underside of the thatch itself, either in an earth daub or a lime plaster. The torching reduced draughts and created a cleaner internal finish.
  • Boarded Ceilings: Close-boarding above the rafters can be left exposed to the underside and historical examples can be found in 19th century buildings.
  • Lath and plaster ceilings: Many roofs were under-drawn with ceilings made of earth or lime plaster applied onto laths fixed to the underside of the rafters. In many cases the plaster is contemporary with the construction of the building and is an important part of its history.

Any historic internal finishes such as these on the underside of pitched roofs should be retained, wherever possible.

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